Understanding of the pathogenesis of enterohemorrhagic E. coli (EHEC) infection has been hindered by the lack of an animal model that effectively reproduces the typical human colonic disease that progresses to the hemolytic-uremic syndrome (HUS). A variety of animal models have been developed to facilitate the study of the gastrointestinal disease or the renal disease caused by these organisms, but not both. These models have disadvantages, including the difficulties of working with infant or gnotobiotic animals, the lack of responsiveness to certain EHEC strains, and the requirement of specific interventions, such as antibiotic treatment prior to animal infection, which add artificial steps to the model. We propose to increase the understanding of disease pathogenesis by developing new mouse models of EHEC infection. Specific Aim 1. Evaluation of the use of Citrobacter rodentium expressing Slliga toxin (Stx) in a mouse model of EI-I.C infection. C. rodentium is a naturally occurring pathogen of laboratory mice, causing transmissible murine colonic hyperplasia. Colonic histopathology of mice infected with C. rodentium show the typical attachment and effacement (A/E) lesion seen in EHEC infection. Strategies have been developed to lysogenize C. rodentium with antibiotic-marked Stxl-, Stx2-, and hybrid Stx-expressing bacteriophages. Toxin production, phage induction, and lysogen stability will be examined in vitro. Mice will be challenged with Stx-producing C. rodentium and will be evaluated for clinical and histopathologic signs of disease. This model has the potential for reproducing both the gastrointestinal and renal injury seen in human disease and for using mouse genetics to examine host factors in the development of EHEC disease. A mouse model would increase our ability to test the efficacy of new therapeutics against EHEC infection. Specific Aim 2. Evaluation of the use of globotriaosylceramide (Gb3)-over expressing mice as a mouse model for ENEC infection. Gb3 is the receptor for Stx. We hypothesize that over expression of Gb3 in the mouse will cause increased sensitivity to Stx. We propose to examine the clinical response and histopathology of Gb3-overexpressing mice injected with purified toxin and infected with toxin-producing strains of E. coli and C. rodentium and to develop this strain as a model for studying the pathogenesis and prevention of EHEC disease.